Esters of phthalic acid are used in large amounts as plasticizers, in particular for polyvinyl chloride. The alcohol components are predominantly primary alcohols having 8 to 10 carbon atoms, of which 2-ethylhexanol is currently the most important. Phthalates formed from shorter-chain alcohols provide plasticizers having a good gelling strength. However, their greater volatility is a disadvantage compared to longer-chained compounds. Longer-chain esters, on the other hand, gel more slowly and have less resistance to low-temperatures.
The properties of phthalate plasticizers are influenced by the size of the alcohol molecule and also by the branching of the carbon chain. For example, alcohols with few branches produce ester plasticizers that are particularly valued despite their high low-temperature flexibility. Predominantly linear alcohols having 9 to 10 carbon atoms in the molecule are therefore becoming increasingly important as the alcohol components. A precondition for their use is that they are available in large amounts and are relatively inexpensive.
Throughout the specification and claims, all percents are by weight unless otherwise indicated. According to German Patent 2 855 421, the plasticizers used are phthalates of alcohols having 9 carbon atoms, which are obtained by the oxo reaction of 8 carbon olefins, hydrogenation of the reaction product, and esterification of the resulting 9 carbon alcohols with phthalic anhydride. From 3% to 20% of the starting olefins should have an isobutane skeleton in each molecular chain, less than 3% of the olefins contain quaternary carbon, and more than 90% of the total amount of the olefins are present as n-octenes, monomethylheptenes, and dimethylhexenes. Furthermore, the weight ratio of the total amount of n-octenes and monomethylheptenes to the dimethylhexenes should be more than 0.8.
Phthalates based on 10 carbon alcohols are the subject of European Patent Application 366,089. These alcohols are used as a mixture obtained by hydroformylation of a butene fraction, aldol condensation of the resultant aldehyde mixture, and subsequent hydrogenation.
Another route for obtaining di-decyl phthalate mixtures is described in European Patent Application 424,767. The esters are prepared by a multistage process involving dimerization of butene mixtures, hydroformylation and hydrogenation of the resulting octene mixture to form a nonanol mixture, dehydration of the nonanol mixture to form a nonene mixture, and hydroformylation and hydrogenation of the nonene mixture to a mixture of decanols.
The known processes still do not satisfy, as regards economic and technical aspects, all requirements that are placed on a process employed on a large scale. The starting materials are not available in sufficient amounts, they are too expensive, and/or the conversion of the starting materials into the alcohols involves processes that are too complicated. The object of the invention is, therefore, to develop a process that starts from raw materials that are available at a reasonable price and which can be converted into the desired alcohols in a technically simple manner.